Such an exhaust gas purifying device is in particular known from U.S. Pat. No. 8,371,114. Such a device is provided to equip an internal combustion engine, for example a diesel engine. It includes a catalyst provided to reduce the nitrogen oxides present in the exhaust gas and an injector placed upstream from the catalyst. The injector is designed to inject a reagent, in particular a reducer or a substance producing a nitrogen oxide reducer, such as urea. The urea undergoes two consecutive chemical reactions, thermolysis and hydrolysis, and turns into ammonia. Within the catalyst, and when the exhaust gases reach a certain temperature, the ammonia reacts chemically with the nitrogen oxides, reducing them into nitrogen and water.
However, this type of device does not make it possible to obtain a sufficient conversion effectiveness of the nitrogen oxides. Indeed, in this type of device, the exhaust gas flow only has a small distance to mix with the urea before reaching the catalyst, which does not allow good homogenization of the mixture.
In this context, the invention aims to propose a device for purifying exhaust gas having a high conversion effectiveness for the nitrogen oxides.